256. PROFESSOR K. OLSZEWSKi ON THE 
external heat. After the liquid oxygen had been thus poured under atmospheric 
pressure, a great part of it evaporated, but there still remained about 70 cub. centims., 
boiling under atmospheric pressure. A calibrated tube, intended to receive the argon 
to be liquefied, and the hydrogen thermometer were immersed in the boiling oxygen. 
At this temperature (— 182°-7*) on admitting argon, no appearance of liquefaction 
could be noticed, even when compressed by increasing the atmospheric pressure by a 
quarter. This shows that its boiling-point lies below that of oxygen. But on 
diminishing the temperature of the liquid oxygen below — 187°, the liquefaction of 
the argon became manifest. When liquefaction had taken place, I carefully equalised 
the pressure of the argon with that of the atmosphere, and regulated the temperature, 
so that the state of balance was maintained for a long time. This process gives the 
boiling-point of argon under atmospheric pressure. Four experiments gave the 
numbers: — 186°7, — 186°°8, —187°0, and — 187°°3. The mean is — 186°9, 
which I consider to be the boiling-pomt under atmospheric pressure (740°5 millims.). 
The quantity of argon used for these experiments, reduced to normal temperature 
and pressure, was 99°5 cub. centims.; the quantity of liquid corresponding to that 
volume of gas was approximately 0-114 cub. centim. Hence the density of argon at 
its boiling-point may be taken as approximately 1°5. Two other determinations of 
the density of liquid argon, for which I employed still smaller quantities of the gas, 
yielded rather smaller numbers. Owing to the small amount of argon used for these 
experiments, the numbers given cannot lay claim to great exactness ; yet they prove 
that the density of liquid argon at its boiling-point (— 187°) is much higher than 
that of oxygen, which I have found, under similar conditions, to be 1:124. 
By lowering the temperature of the oxygen to — 191° by slow exhaustion, the 
argon froze to a crystalline mass, resembling ice; on further lowering temperature it 
became white and opaque. When the temperature was raised it melted ; four obser- 
vations which I made to determine its melting-point gave the numbers: — 189°-0, 
— 190°6, — 189°°6, and — 189°°4. The mean of these numbers is — 189°°6; and 
this may be accepted as the melting-point of argon. 
In the following table I have given a comparison of physical constants, in which 
those of argon are compared with these of other so-called permanent gases. The data 
are from my previous work on the subject. 
* T have re-determined the boiling-point of oxygen, using large quantities of oxygen, and a hydrogen 
thermometer of much larger dimensions than previously. The registered temperature is 1°°3 lower than 
that which I previously recorded, 
